1. Field of the Invention
The present invention relates to the field of nanomaterials such as carbon nanotubes and further to the field of molecular sized electromechanical devices.
2. Related Art
Nanostructures are of great interest not only for their basic scientific richness, but also because they have the potential to revolutionize critical technologies. The miniaturization of electronic devices over the past century has profoundly affected human communication, computation, manufacturing and transportation systems. True molecular-scale electronic devices are now emerging that set the stage for future integrated nanoelectronics (Ref 1).
Recently, there have been dramatic parallel advances in the miniaturization of mechanical and electromechanical devices (Ref 2). Commercial microelectromechanical systems now reach the submillimeter to micrometer size scale, and there is intense interest in the creation of next-generation synthetic nanometer -scale electromechanical systems (Refs 3,4). Such a nanometer scale electromechanical system is described below, demonstrating the construction and successful operation of a fully synthetic nanoscale electromechanical actuator/motor incorporating a rotatable metal plate, with a multi-walled carbon nanotube serving as the key motion-enabling element.
Although devices have been made by scaling down existing microelectromechanical systems (MEMS), the workhorse methods and materials of MEMS technology are not universally well suited to the nanoscale. Ultra-small silicon-based systems fail to achieve desired high-Q mechanical resonances owing to dominant surface effects and thermoelastic damping, and limitations in strength and flexibility compromise silicon-based high-performance actuator/motors (Refs 5, 6). On the other hand, the unusual mechanical and electronic properties of carbon (Ref 7) and boron-nitride (Ref 8) nanotubes (including favorable elastic modulus and tensile strength, high thermal and electrical conductivity, and low inter-shell friction of the atomically smooth surfaces (Refs 9, 10) suggest that nanotubes may serve as important NEMS-enabling materials if nanotubes can be engineered and modified to be part of a higher order system, i.e. as active components in a movable device.
Cumings et al. US 2002/0070426 A1 discloses a method for forming a telescoped multiwall carbon nanotube (“MWNT”). Such a telescoped multiwall nanotube is shown in this publication to act as a linear bearing in an electromechanical system. That is, the walls of a multiwalled carbon nanotube are concentrically separated and are shown to telescope axially inwardly and outwardly. In Science 289:602–604 (28 Jul. 2000), a scientific publication related to the 2002/0070426 A1 patent publication, Cumings and Zettl describe a low friction nanoscale linear bearing, which operates in a reciprocal (i.e. telescoping) manner.
Den et al. U.S. Pat. No. 6,628,053 discloses a carbon nanotube device comprising a support having a conductive surface and a carbon nanotube, wherein one terminus of the nanotube binds to the conductive surface so that conduction between the surface and the carbon nanotube is maintained. The device is used as an electron generator.
Falvo et al. Nature 397:236–238 (Jan. 21, 1997) disclose studies involving the rolling of carbon nanotubes using atomic force microscope (AFM) manipulation of multiwall carbon nanotubes (MWCNT, termed in the paper “CNT”). No bearing properties are disclosed.
Minett et al. Current Applied Physics 2:61–64 (2002) disclose the use of carbon nanotubes as actuators in which the driving force is obtained from a deformation of the nanotube when a charge is applied. The authors, in their review also disclose the preparation of a suspended carbon nanotube across two metallic contacts growth of nanotubes across two metal contacts in a process that involved E-beam lithography and selective patterning.
Cumings et al. Nature 406:586 (Aug. 10, 2000) disclose techniques for peeling and sharpening multiwall nanotubes. These sharpened tubes are disclosed as having utility as biological electrodes, microscopic tips, etc.
Fraysse at al. Carbon 40:1735–1739 (2002) discloses carbon nanotubes that act like actuators. In concept, a SWNT may be disposed above a substrate and between a pair of metal-on-oxide layers. The nanotubes act as actuators through a cantilever effect achieved through longitudinal deformation of the nanotube.